The present invention relates to an electrode for a ceramic flow tube used in a magnetic flow meter, and which provides for high resistance to abrasion or erosion by the flowing fluid and which can be made in a manner to remain fluid tight.
Magnetic flowmeter electrodes are a source of continuing development in magnetic flowmeters using a ceramic flow tube. In prior art devices, a ceramic flow tube is formed and then electrodes of various kinds are placed into the wall of the tube. Sintering fixes the electrodes in place, but the ability to obtain leak tight electrodes plagues designers. In some instances, in the sintering of the measuring pipe with the electrodes in place in bores in the tube wall, the electrode material will not withstand the sintering temperature of ceramics, or will have a different thermal co-efficient from ceramics. Platinum electrode materials are used, as well as conductive ceramic materials. Electrodes using a ceramic core rod having a conductive portion of a refractory metal that covers the fluid contact end face of the rod and extends outward on the rod so that it can be connected to a lead, have been advanced as well. The use of metal coatings on ceramic rods solves some problems of sintering the materials in place, but there still are problems of erosion of the faces that are in contact with the fluid flowing through the flow tube.